Segment Reporting, Identifiable Assets by Industry Segment (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Segment Reconciliation [Abstract]
Total assets	$ 248,529	$ 246,872
Reportable segments
Segment Reconciliation [Abstract]
Total assets	248,529	246,872
Reportable segments | Marketing
Segment Reconciliation [Abstract]
Total assets	107,388	107,257
Reportable segments | Transportation
Segment Reconciliation [Abstract]
Total assets	29,492	32,120
Reportable segments | Oil and Gas (1)
Segment Reconciliation [Abstract]
Total assets	3,200	7,279
Corporate non-segment
Segment Reconciliation [Abstract]
Total assets	$ 108,449	$ 100,216